Centrifugal biological-fluid-processing systems have been in existence for some time. Some are used to collect high concentrations of certain components of a person's blood while others are used to further process blood components by washing, concentrating or otherwise purifying the blood component of interest. Some of these systems are used to process biological fluids other than blood. Filtration systems are also used for processing blood and other biological fluids.
The centrifugal systems (hereinafter called blood-processing systems) generally fall into two categories, continuous-flow devices and discontinuous-flow devices.
In continuous-flow systems, whole blood from the donor or patient flows through one conduit into the spinning rotor where the components are separated. The component of interest is collected and the unwanted components are returned to the donor through a second conduit on a continuous basis as more whole blood is being drawn. Because the rate of drawing and the rate of return are substantially the same, the extracorporeal volume, or the amount of blood that is out of the donor or patient at any given time in the procedure, is relatively small. These systems typically employ a belt-type rotor, which has a relatively large diameter but a relatively small (typically 100 ml or less) processing volume. Although continuous-flow systems have the advantage that the amount of blood that must be outside the donor or patient can be relatively small, they have the disadvantage that the diameter of the rotor is large. These systems are, as a consequence, large; furthermore, they are complicated to set up and use. These devices are used almost exclusively for the collection of platelets.
In discontinuous-flow systems, whole blood from the donor or patient also flows through a conduit into the rotor where component separation takes place. These systems employ a bowl-type rotor with a relatively large (typically 200 ml or more) volume that must be filled with blood before any of the desired components can be harvested. When the bowl is full, the drawing of fresh blood is stopped, and the unwanted components are returned to the donor or patient through the same conduit intermittently, in batches, rather than on a continuous basis. When the return has been completed, whole blood is again drawn from the donor or patient, and a second cycle begins. This process continues until the desired amount of component has been collected.
Discontinuous-flow systems have the advantage that the rotors are relatively small in diameter but have the disadvantage that the extracorporeal volume is large. This, in turn, makes it difficult or impossible to use discontinuous systems on people whose size and weight will not permit the drawing of the amount of blood required to fill the rotor. Discontinuous-flow devices are used for the collection of platelets and/or plasma, and for the concentration and washing of red blood cells (RBCs). They are used to reconstitute previously frozen RBCs and to salvage RBCs lost intraoperatively. Because the bowls in these systems are rigid and have a fixed volume, however, it is difficult to control the hematocrit of the final product, particularly if the amount of blood salvaged is insufficient to fill the bowl with RBCs.
One RBC-washing system marketed by Cobe Laboratories is made almost entirely of flexible PVC. It has the advantage of being able to vary the volume of the rotor to control the final hematocrit but has the disadvantage of being limited to a rather flat, wide pancake-like shape due to manufacturing constrictions. The Cobe system controls the rotor volume by pumping a hydraulic fluid--a liquid--in or out of a bladder that rotates with and squeezes the blood out of rotor. The Cobe system takes up a fairly large amount of space, and its flexible pancake-shaped rotor is awkward to handle. The Cobe system does not permit blood to flow into and out of its rotor at the same time. The Cobe system also does not permit blood to be pulled into the rotor by suction. The Cobe rotor is usually filled with blood by gravity, although the blood may be pumped into the rotor. After the blood has been separated, it is squeezed out of the rotor by pumping hydraulic fluid into the bladder.
Haemonetics Corp. and others have provided systems to collect blood shed during surgery, concentrate and wash the RBCs, and return them to the patient. Existing systems typically use a 3 liter reservoir to collect and coarse filter the blood vacuumed from the surgical site and a separate processing set including a special centrifugal processing chamber to wash and concentrate the red blood cells in order that they may be safely reinfused to the patient. Because of their cost and complexity of use, these systems are used only in operations where relatively large blood loss is expected. The prior-art rotors used for processing blood collected during an operation, made by Haemonetics Corp. and others, must be completely filled with RBCs before any processing can occur, and thus the process takes more time and is not appropriate for use with small people or for an operation with low blood loss. Because the volume of the processing chamber is fixed, the final concentration of the RBCs in the last cycle of the process cannot be easily controlled.
Solco Basel AG makes a filter-based system for wound drains. This wound-drain system has the disadvantage that the blood returned to the patient contains, in addition to the RBCs, substances that may be deleterious to the patient.
There exists the need, therefore, for a centrifugal system for processing blood and other biological fluids, that is compact and easy to use and that does not have the disadvantages of prior-art discontinuous-flow systems. There is also a need for improving the way that blood is processed in a variety of applications, such as apheresis, intraoperative blood-salvage systems, and wound drains, so that the blood processing takes less time, requires less cumbersome equipment, and/or reduces harmful side effects in the patient or donor.